31 lines
865 B
Plaintext
31 lines
865 B
Plaintext
defmodule Statistics do
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def normal_distribution(n, w\\5) do
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{sum, sum2, hist} = generate(n, w)
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mean = sum / n
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stddev = :math.sqrt(sum2 / n - mean*mean)
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IO.puts "size: #{n}"
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IO.puts "mean: #{mean}"
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IO.puts "stddev: #{stddev}"
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{min, max} = Map.to_list(hist)
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|> Enum.filter_map(fn {_k,v} -> v >= n/120/w end, fn {k,_v} -> k end)
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|> Enum.min_max
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Enum.each(min..max, fn i ->
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bar = String.duplicate("=", trunc(120 * w * Map.get(hist, i, 0) / n))
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:io.fwrite "~4.1f: ~s~n", [i/w, bar]
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end)
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IO.puts ""
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end
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defp generate(n, w) do
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Enum.reduce(1..n, {0, 0, %{}}, fn _,{sum, sum2, hist} ->
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z = :rand.normal
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{sum+z, sum2+z*z, Map.update(hist, round(w*z), 1, &(&1+1))}
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end)
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end
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end
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Enum.each([100,1000,10000], fn n ->
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Statistics.normal_distribution(n)
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end)
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